This invention relates to an alloy and a method of producing the same.
In order to provide hard amorphous alloys, bulk metallic glass and nanocrystalline alloys with high plastic deformability, it is effective to finely disperse a soft metallic phase, which is easy in plastic deformation, in the alloy. In most of the amorphous alloys and nanocrystalline alloys which manifests high strength and high toughness, perfect adherence bending (i.e., 180-degrees bending without breaking) is possible in a thin film state and 100% plastic extensional deformation is realized on a bending surface although these alloys are hard materials. However, when a tensile test is performed on these alloys, the plastic deformation is locally generated and brittle fracture is caused even by very slight elongation. Presumably, this is because these materials do not exhibit work hardening and plastic deformation locally progresses.
Therefore, in order to provide hard amorphous alloys, bulk metal glass and nanocrystalline alloys with high plastic deformability, it is required to widely and finely disperse the soft metallic phase, which is easy in plastic deformation, as a plastically deformable region in the alloy, thereby stopping the local progress of the plastic deformation and dispersing the plastic deformation. Thus, high plastic elongation is expected upon tensile deformation.
Under the circumstances, it has been tried to form a nano-scale composite structure obtained by finely dispersing precipitated phases which have a good coherency with a parent phase (see A. Inoue et al., “Formation and properties of Zr-based bulk quasicrystalline alloys with high strength and good ductility”, J. Mater. Res., Vol. 15, No. 10 (2000), pages 2195-2208).
Referring to FIG. 1, an alloy structure comprises a bulk metallic glass as a parent phase and a quasi-crystalline phase well coherent with the parent phase and finely dispersed in the metallic glass. For this alloy structure, some improvement in plastic deformability upon compressive deformation is reported. However, plastic workability of a dispersed precipitated phase with a quasi-crystalline structure is bad. As shown in the illustrated example, it is difficult by known methods using heat treatment and the like to intentionally disperse the soft precipitated phase having both coherency with the parent phase and high plastic deformability in hard amorphous alloys, bulk metallic glass and nanocrystalline alloys.
On the other hand, in the electrodeposition (i.e., electrolytic deposition) method, it is possible by controlling a potential or a current density to electrodeposit only depositable alloys or atomic elements. It is known so far that a Ni(nickel)—W(tungsten) nanocrystalline alloy produced by using the electrodeposition method exhibits high strength and high toughness. Specifically, the perfect adherence bending is possible and the tensile fracture strength exceeds 2000 MPa (T. Yamasaki, “High-strength nanocrystalline Ni—W alloys produced by electrodeposition and their embrittlement behaviors during grain growth”, Scripta mater. 44 (2001), pages 1497-1502).
By locally depositing nickel on a substrate by electrodeposition using a needle-like single-anode electrode and precisely moving the position of the needle-like electrode in synchronization with an electrodeposition rate, columnar and helical three-dimensional structures made of nickel with a diameter of 10 microns and a height of 100 microns were produced (John D. Madden and Jan W. Hunter, “Three-Dimensional Microfabrication by Localized Electrochemical Deposition”, Journal of Microelectromechanical Systems, Vol. 5, No. 1, March 1996, pages 24-32). However, this method is different from the technique of artificially controlling local structures and compositions in an electrodeposited material throughout the whole electrodeposited material and does not create a bulk alloy having high strength and high ductility.
It is extremely difficult to successfully form the above-mentioned dispersed phase only by adjusting a heat treatment condition that determines the composition of the amorphous alloy and its partial crystallization. In many cases, the embrittlement is caused by the heat treatment. Therefore, the structure of the alloy produced by the conventional technology is far different from an ideal composite structure of the nanoscale and achieves neither the expected strength nor the expected plastic deformability.
On the other hand, the nanocrystalline Ni—W alloy produced by the conventional electrodeposition method has high strength and high toughness, but its rupture elongation under tension is not greater than 0.5%. Thus, the Ni—W nanocrystalline alloy has the same defect as the amorphous alloy or the nanocrystalline alloy produced by the conventional rapid quenching technique from the liquid state, etc.